Constant-current motor



(No Model.) 5 Sheets Sheet l.

W. BAXTER, Jr. CONSTANT CURRENT MOTOR.

. No. 423,897. Patented Mar. 25, 1890.

a. PG! MW. WM, DJ;

(No Model.) 5 Sheets-Sheet 2.

W. BAXTER,- Jr. CONSTANT CURRENT MOTOR.

(No Model.) 5 Sheets-Sheet 3.

. W. BAXTER, Jr.

CONSTANT CURRENT MOTOR.

-No. 423,897. Patented Mar. 25, 1890.

(No Model.) 5 Sheeta-Shaet 5.

W. BAXTER'. Jr.

CONSTANT CURRENT MOTOR.

No. 423,897. Patented Mar. 25. 1890.

11 fir/7572 7507; v w. Wm; 75M;

UNITED STATES PATENT OFFICE.

VILLIAM BAXTER, J Pu, OF BALTIMORE, MARYLAND.

CONSTANT-CU RRENT MOTOR.

SIEECIFICA'IION forming part of Letters Patent No. 423,897, dated March25, 1890.

Application filed March 22, 1889. Serial No. 304,025. (No model.)

To all whom it may concern:

Be it known that 1, WILLIAM BAXTER, J r., a citizen of the UnitedStates, residing at Baltimore, Maryland, have invented certain new anduseful Improvements in Constant-Ourrent Motors, fully described andrepresented in the following specification and the accompanyingdrawings, forming a part of the same.

The object of this invention is partly to furnish an improved method andmeans for regulating a constant-current motor having the fieldmagnetized by a current shunted from the surface of the commutator.

The invention consists in a constant-current motor having the fieldmagnetized by a current shunted from the commutator through two brushesattached to the terminals of the field-coils and adaptedfor changing theelectrical relation of the brushes to one another automatically by acentrifugal governor rotated in unison with the motor-armature, andtherefore affected by the load upon the motor.

The invention also consists in the combination, with the commutator, thefield-coils, and the brushes combined therewith, as just described, of apeculiarly-constructed switch required for operating a motor of thisclass.

I-Ieretofore it has been common in constantcurrent dyn amo-electricalmachines to employ various arrangements of brushes in which one or moreadjustable brushes have been combined with one or more fixed brushes toshunt a variable current from the surface of the commutator through thefield-coils for maintaining a constant current in the armature-circuitunder a variable resistance. In such case the speed of the machine issupposed to be uniform at all times, being governed exclusively by themotive power applied to rotate the armature, and not affected in anymanner by variations in the field-circuit or the armature-circuit. Anyof the various arrangements heretofore used for shunting a current fromthe surface of the commu tator may be employed in practicing myinvention; but I prefer the arrangement in which one terminal of thefield is attached to one of the stationary brushes and the other isattached to a movable brush.

As a governor is essential to my present invention, and as the governoris employed to vary the electrical relation of the brushes to which theterminals of the field-coils are attached, it is obvious that itinvolves less mechanical complication to use but a single movable brushand to actuate the same by the governor.

My improvements will be understood by reference to the annexed drawings,in which- Figure 1 is an end elevation of a motor having theswitch-board fixed upon a bridge between. the pole-pieces; but theswitch-lever and fixtures are omitted for want of room upon thedrawings. Fig. 2 is a side elevation of the same parts with the switchand switch-board removed from the pole-pieces and the bearing for thearmature-shaft broken off at the right-hand end. Fig. 3 is a centralvertical section of the magnet-cores and polepieces transverse to theaxis of the armature, with the bed (not in section) attached to thebases of the magnet-cores. Fig. at is a plan of the switch, with adiagram of the armature and the field-coils and their connections. Fig.5 is a side elevation of the switch and the bridge by which it isattached to the polepieces, with the resistance-box and its contacts insection on line in Fig. 4. Fig. 6 is a plan of the bed with the motordetached therefrom. Fig. 7 is a vertical section of the governor, takenon its center line. Fig. Sis a view of the outer end of the governorwith the shell removed. Fig. 9 is a plan of the governor in section atits'center line. Fig. 10 is an inside view of the governor-shell; andFig. 11 is a section of the same similar to that shown in Fig. 7, butdetached from the governor-head. Fig. 12 is a plan of the governorshaftviewed as in Fig. 9, but not in section. Fig. 13 is an inside view ofthe governor-head, with the shaft in section on line .2 .2" in Fig. 7,and Fig. ll is a side View of the governorhead detached. Figs. 15, 1G,and 17 are diagrams of the switch and circuit connections.

In the motor, C are the magnet-cores, O flanges at their bases, and Cthe pole-pieces. The cores are projected vertically from the bed B,which is shaped upon the top to fit the flanges C and the feet of thestandards D forthe armatore-bearings. The top of the bed is therefore ofrounded out-line at the points where the flanges O are secured; but thebed is provided at the bottom with lateral flanges 11', having paralleledges to adapt the bed for sliding in the ways to which such motor-bedsare fitted to render them movable for tightening the attached belt. Theparallelism of the opposite sides of the bed at the lower edge is anessential partof my construction, while the form at the top of the bedis immaterial. The cores C are secured to the bed by studs 3 extended upinto the pole-pieces and provided at various points with transverse pins0. The lower end of the stud is projected below the flange B a suit-abledistance to pass through the web of the bed and receive a screw-threadand nut B upon its lower end. The studs are secured within the cores bysupporting the studs in a mold and pouring the melted iron into the moldaround the stud, the pins 0* serving to hold the stud securely withinthe casting, which cannot always be effected by the mere shrinkage ofthe cast metal upon the stud. Holes B are formed in the bed to receivethe studs, and the under side of the bed is provided with recesses B tocontain the nuts B A is the armature, A the armature-shaft, and A thecommutator adjacent to the armature-bearin g D. The shaft is extendedthrough the bearing and provided with a governor of unusually smalldimensions contained within a shell 8, secured by a screwthread upon theperiphery of a head t, and both the head and shell being movablelongitudinally upon the shaft. The armaturecircuit brushes 6 and e areshown mounted in swinging holders f, pivoted upon lugs g, which aresecured upon and insulated from cars g upon the bearing D. The movablebrush a is carried in a holder to, pivoted upon a stud d, which is fixedby insulated fastenings upon a swinging frame pivoted at one side of thebearing D. The frame is formed with a seat cl and arms h, mounted uponpivots z', fitted in ears j, one at the inner and one at the outer sideof the bearing D, and the frame is provided with a roller 7t, adapted tobear upon the conical back: of the head If. The brush a is mounted tobear upon the commutator adjacent to the brush 6, and these two brushesare connected, respectively, with the terminals of the fieldmagnetcoils. A spring it operates upon the frame to press the roller is towardthe shaft A and the longitudinal movement of the governor upon the shafttoward the roller presses the conical face of the head against theroller and forces it outward from the shaft. Such outward movement ofthe frame shifts the movable brush a nearer to the brush 6, and,

.as the potential varies upon the surface of the commutator between thetwo brushes, such movement produces a Variation in the current shuntedfrom the commutator through the field-coils and affects the strength ofthe field in the desired manner.

The head of the governor i has a groove Z slotted radially across itsinner surface, and arms Z are pivoted in the outer ends of such groovewith their inner ends fitted to a hole or slot m, forming abutments m inthe armature-shaft. The arms are provided with weights a, projected atright angles to the arms, and thus moved to and from the shaft by avibration of the arms upon their pivots. The shell incloses the weightsand arms and is provided at its outer end with a bush 0, fitted to athread in the end of the shell, so as to be adjustable to and from thehead If. A shoulder t is formed upon the shaft adjacent to the hole m byreducing the size of the shaft from that point outward through the bush0, and a spiral spring a is fitted between the bush and the shoulder topush the governor normally toward the end of the shaft. The weights nare curved externally to closely fit the interior of the shell 3 and arenotched internally to fit closely around the spring to secure themaximum of weight within the desired compass. The head f, is movablelongitudinally upon the shaft, but is rotated therewith by theengagement of the arms I with the abutments m in the hole m, and theexpansion of the weights when rotated therefore operates to change theannular position of the arms in relation to the hole, and by theresultant pressure upon their pivots forces the head toward the roller kin opposition to the tension of the spring a. The spring is providedwith an adjustingscrew k by which its pressure upon the frame thatcarries the brush a may be varied at pleasure, so as to increase ordecrease the ten: sion with which the roller 7; resists the longitudinalmovement of the governor. The bush 0, when adjusted in the outer end ofthe shield, also serves to vary the tension of the spring wand to thusvary the speed at which the governor would act upon the frame of thebrush a. By the adjustment of these two springs a and k it is possibleto regulate the governor so as to operate upon the brush a at anyvelocity at which it maybe desired to run the motor, and also to adjustthe proportion of the centrifugal force of the governor that is to beresisted by either one of the springs. These adjustments are of greatvalue, because it is frequently desired to vary the normal velocity ofthe machine, and also because it is necessary that the spring 7c',whichpresses against the brush-frame, should have enough tension to press thebrush forward, and at the same time not have too much, because thetension of this spring as it pushes against the conical surface of thegovernor results in moving the whole shaft endwise, and thus imposes acertain thrust upon some of the shaft-bearings and produces anunnecessary amount of frictional resistance to the rotation of thearmature.

In a motorof this class, unless some artificial resistance is used inthat portion of the motorcircuit which is shunted to the field when themotor starts, it would be impossible to set it in motion unless runningfree or with a very light load. This is due to the fact that the portionof the armature-coils that is shunted by the field is very small, itsresistance is very low, and the current that it would shunt through thefield when unaided by its counter electro-motive force would nottherefore be suflicient to produce the strength of field necessary tomake the armature rotate; To introduce such resistance in the propermanner, I have devised a special construction of switch provided withthree contacts, a resistance, and a movable lever. hen the lever ismoved from the first contact to the second, it closes the 'circuitthrough the motor and interposes a resistance in that portion of thearmature-circuit which is shunted by the field. This causes alargecurrent to pass through the field and to magnetize it sufiiciently toset the armature in motion under any suitable load. As soon as thearmature has assumed a speed sufiicient to give it the requisite counterelectro-motive force to maintain the current in the field the lever ismoved farther, so as to reach the third contact while remaining upon thesecond. In this position it establishes a direct connection between thesecond and third contacts and short-circuits the resistance previouslyin the circuit. I use for the resistance in this switch a compactcylindrical case 11, of metal, in which is inclosed a block or mass oflamp-black R, or any other,

substance of high resistance. This is simply for the purpose of makingit compact. It is evident, however, that if neatness and compactnesswere not considered any substance whatever that would ofier resistanceto the on rrent would answer the purpose. The switch is shown in Figs. 4and 5, in which G is a bedplate attached to a bridge G, secured be tweenthe two pole-pieces, as shown in Fig. 1.

Binding-posts t 5 6 7 are provided near one end of the bed-plate, withthe posts et and 7 connected with the armature-brushes e and c. The post5 is connected with one of the fieldcoils F, and the other field-coil Fis connected with the movable brush a through the binding-post 6. Astuds is mounted near the center of the bed to serve as a pivot for thelever 9,and is connected by strip 2 and binding-post 14 with one of theline-conductors.

. wide enough to overlap two of the contacts at is placed upon contact1, as shown in Figs. 1 and 15. The motor therefore receives no currentuntil the lever is moved to contact 2 in circuit with the resistance, asshown in Fig. 1G. \Vere the resistance not interposed in the connectionfrom this contact to the brush 6, the entire current would flow throughthe armature, and the field would ,not be sufliciently magnetized tostart the motor under a load. The resistance, however, causes thecurrent to divide, one part, as indicated by the arrows J, going to thefield-coils F F and brush a, while the other part, as indicated by thearrows I, passes through the resistance to contact 3 and brush e. Inthis position of the lever the field shunts the resistance R and theresistance is in series with the portion of the armature thus shunted.

In the third position of the lever shown in Fig. 17, to which positionthe lever-is moved when the motor is fully under way, the resistance iswholly cut out by the contact of the cross-head 13 with contacts 2 and3, and the current divides in leaving the lever according to theresistances of the field and armature coils, a portion of the currentpassing directly to the brush a by arrows K and a portion to thefield-coils by arrows L. In this third position of the switch-lever thefield shunts that portion of the armaturecoils included between thecommutator-sections with which the brushes a and e are in contact, andthe counter electro-motive force of such portion of the armature-coilsdetermines the proportion of current that-is shunted by the field.

An increase of load upon the motor causes a temporary decrease in thespeed of the same, thereby causing the governor to move the brush anearer the brush 6. Such operation of the governor causes an increase inthe strength of the field, thereby bringing the speed of the motor up tothat acquired before the increased load was applied.

It will be understood from the above description that it is necessaryfor the positive line-conductor to be connected with the fieldcoils atall times when the motor is in operation, and that the cross-head 13,which c011- veys the current from such line-conductor, must therefore beso constructed that it may remain upon contact 2 after it is shifted tocontact 3, for which reason the cross-head is made of suitable width toreach from one contact to the other. The whole lever may be.

made of suitable width and no cross-head be may always find a coursewithout interniedi-- ate resistance to the field-coils, while it isunable to pass directly to the brush (2 until the cross-head is moved tothe contact 3. The

essential feature of my switch constructionis, therefore, thecombination of the contact 2, connected directly to the field-coils andFor the same reason the contact through the resistance to the brush 6,with the contact 3, connected directly to the said brush, the wholeoperating to throw a great proportion of the current into the field instarting the motor and to cut out the resistance when the switch-leveris shifted to the contact 3 after the motor is fully started. It willalso be seen from the above description that the operation of myconstruction differs essentially from that of a dynamo-electric machine,in which the speed is controlled and kept uniform by forces whollyoutside of the electrical conditions, and the strength of the current orits potential is regulated by automaticagencies.

In my construction the strength of the cur-- rent or its potential isnot affected by any automatic mechanism, but is controlled by meansentirely outside of the electrical conditions within the motor, whilethe speed is regulated by the automatic operation of a governor actingthrough the movable brush. The movable brush thus performs a function inthe motor different from that which it exercises in a dynamo-electricalmachine, as it operates exclusively to maintain a uniform speed of thearmature, and is not used to affect the current operating in theline-circuit with which the motor is connected. To regulate the speed inthe desired manner, it is necessary that the movable brush a should beable, when required,'to bear upon the same section of the commutator asthe adjacent fixed brush 2, and the entire mechanism for shifting thebrush a is therefore constructed to move past the holder f of the brush6-. The commutator is therefore made wide enough to accommodate the twobrushes side by side, as shown in Fig. 2, and the entire brushholder at,as well as the stud d and the frame which carries it, is constructed tomove past the brush-holder f, as is shown in Figs. 1 and 2. Suchoperation is secured by mounting the stud f, upon which the holder f ispivoted, upon the lug g at a greater distance from the center of thearmature than the frame d,

.When the frame carrying the movable brush is swung backward by theaction of the governor, it is thus enabled not only to be brought intoline with the brush 6, but to move back of the same, so as to reversethe current through the armature in case the load upon the motor issuddenly thrown off. An extravagant speed is thus prevented, as well asany derangement in the circuit with which it is connected.

It willbe'noticed by reference to Figs. 3 and 6 that the top of the bedupon which the standards D and cores 0 are secured is perfectly flat,thus reducing the cost of 0011- structing and fitting the joints. Thetop has an outline corresponding with the bases of the standards and theflanges of the cores, while the bottom of the bed, as shown in Fig. 6,is of rectangular form, with parallel sides to slide in the ways towhich such motorbeds are commonly fitted, and the bed intermediate tothe top and bottom surfaces is formed, as shown in Figs. 3 and 6, withsloping surfaces uniting the outlines of the top and bottom. Lugs D areformed upon the bed between the seats and provided with tapped holes Dto receive bolts D for securing the standards to the bed.

The expansion of the cores at their lower ends into the flanges Cgreatly increases the surface of contact at the joint between the bedand core, and thus reduces the magnetic resistance.

It will be noticed in Fig. 5 that the block of resistance material R isinsulated from the sides of the case ll by a layer of suitableinsulating material 10. The case 11 is connected with the contact 3 bythe connection y, and a plate 12, connected with the contact 2, formsone side of the resistance-box, having a metallic projection to pressupon the resistance-block R. The insulating material 10 prevents thecurrent entering by the contact 2v from passing to the connection 1through the sides of the case and restricts its passage to theresistance material R.

The pins 0, inserted through the studs 0, may, if desired, be formed bybundling together several small rods, the ends of which may be readilyseparated, as shown in one of the transverse pins at the left side ofFig. 3, near the top of the stud. A closer connection between the studand the casting is thus secured. 1

Having thus set forth my invention, what I claim herein is 1. In aconstant-current electric motor havin g the field magnetized by acurrent shunted from the face of the commutator, the combination, withthe field-coils, armature-shaft, and its commutator, and a centrifugalgovernoractuated by the motor, of two main commutatorbrushes and one ormore auxiliary brushes, two of the brushes being attached to theterminals of the field-coils, and one or both of the said brushes beingindependent of the main brushes and movable by the governor, thedifference of potential between the brushes connected with thefield-coils being varied by the action of the centrifugal governor forthe purpose of maintaining a constant speed under variations in the loadby changing the strength of the magnetizingcurrent, substantially asshown an d described.

2. In a constant-current electric motor, the means for maintaining thespeed of the armature-shaft constant under variations of the load,consisting in the combination, with the field-coils, the armature, thearmature-shaft,

its commutator, and one or more brushes auxiliary and independent of themain brushes, of electrical connections from two of the brushes to thefield-coils, a centrifugal governor operating in unison with themotor-armature, and suitable connections from the governor to theauxiliary brush or brushes to shift the same upon the surface of thecommutator and thereby vary the difference of potential between thefield-coil brushes, as and for the purpose set forth.

3. In a constant-current electric motor, the means of maintaining thespeed of the armature-shaft constant under variations of the load,consisting in the combination, with the field-coils, the armature, thearmature-shaf t, its commutator, and one or more brushes auxiliary andindependent of the main brushes, of electrical connections from two ofthe brushes to the field-coils, a centrifugal governor located on thearmature-shaft and operating in unison with the motor-armature, andsuitable connections from the governor to the auxiliary brush or brushesto shift the same upon the surface of the commutator and thereby varythe difference of potential between the field-coil brushes, as and forthe purpose set forth. I

4. In a constant-current electric motor, the combination, with thearmature-shaft and its commutator, of a movable brush and a pivotedframe having a projection thereon, the conical governor-head t incontact with such projection and movable longitudinally upon thearmatureshaft, an. abutment, as m formed in' the shaft and provided withradial groove Z coincident with such hole, the weighted arms Z, pivotedin the outer ends of such groove with their inner ends fitted to thehole in the shaft, and a spring operating upon the head in opposition tothe centrifugal force of the weights, as and for the purpose set forth.

5. In a constant-current electric motor, the combination, with thearmature-shaft and its commutator, of a movable brush and a pivotedframe having a projection thereon, the conical governor-head t incontact with such projection and movable longitudinally upon thearmature -shaft, an abutment, as on, formed in the shaft, the shouldert, formed upon the shaft adjacent to the abutment m, the shell 8,attached to the head if for inclosing the governor-weights, the bush 0,fitted loosely to the armature-shaft and screwed in the shell, and thespiral spring a, fitted to the shaft between the bush 0 and the shouldert and operating in opposition to the centrifugal oted frame having aprojection thereon, of the conical governor-head t in contact with suchprojection and movable longitudinally upon the armature-shaft over anabutment, as m, formed in the shaft, and the head provided with radialgroove Z coincident with such hole,.

the arms Z, pivoted in the outer ends of such groove with their innerends fitted to the hole in the shaft, the shoulder 25, formed upon theshaft adjacent to the hole m, the shell 3, attached to the headt andmovable with the head upon the shaft, the spiral spring u, titted to theshaft between the shell and the shoulder 6, and the weights 12, attachedto the arms Z, the weights 02 being shaped externally to fit theinterior of the shell and notched internally to lit around the spring11, as and for the purpose set forth.

7. In a constant-current electric mot-or, the means for maintainingthespeed of the armature-shaft constant under variations of the load,consisting in the combination, with the field-coils, of twocommutator-brushes e and a, connected to the terminals of such coils, apivoted frame carrying one of said brushes, a projection on said frame,a centrifugal governor-head mounted upon the end of the armature-shaftand adapted to move longitudinally, a conical surface upon suchgovernorhead in contact with the projection on said brush-frame, and aspring to press the projection toward such conical surface, as and forthe purpose set forth.

8. In a constant-current electric motor, the means for maintaining thespeed of the armature-shaft constant under variations of'the load,consisting in the combination, with'the field-coils, of twocommutator-brush'es a and 6, attached to the terminals of such coils,the fixed brush 6, the movable brush a being carried upon a movableframe provided with roller 71;, the governor-head t, movablelongitudinally upon the armature shaft adjacent to the roller and havinga conical surface to bear upon such roller, the governor-weights pivotedto such head, and adapted, when rotated, to press the conical surfacetoward the roller, and a spring acting in opposition to the centrifugalforce of the weights, as and for the purpose set forth.

0. I11 a constant-current electric motor, the combination, with amovable brush and a pivoted frame having a projection thereon, of theconical governor-headt in contact with such projectlon and movablelongitudinally upon the armature-shaft over a hole on formed in theshaft, and provided with radial groove Z coincident with such hole, theweighted arms Z, pivoted. in the outer ends of such groove, with theirinner ends fitted tothe hole in the shaft, the shoulder t, formed uponthe shaft adjacent to the hole m, its pivoted frame carrying roller 7.,the head i, provided with shells and movable longitudinally upon theshaft, the shoulder t, formed uponlthe shaftwithin the shell, the spiralspring a, in-

serted between the shoulder and the'outer.

IIO

end of the shell, the weights pivoted upon the head and operating topress the same toward the roller 7a, and the spring is, operating topress the roller toward the conical surface of the head, as and for thepurpose set forth. 10. In a constant-current electric motor, thecombination, with a movable brush and a pivoted frame having aprojection thereon, of the conical governor-head t in contact with suchprojection and movable longitudinally upon the armature-shaft over ahole on formed in the shaft, and provided with radial groove Zcoincident with such hole, the weighted arms Z, pivoted in the outerends of such groove, with their inner ends fitted to the hole in theshaft, the shoulder 25', formed upon the shaft adjacent to the hole on,its pivoted frame carrying roller 7c, the slotted head i, fitted uponthe armature-shaft provided with the hole m, the weighted arms pivotedwithin the slot and having their inner ends fitted to the hole m, theshoulder i upon the armature-shaft adjacent to the hole m, the shell 8,attached to the head if by screw-thread and provided with the adjustablebush 0, the spiral spring a, fitted upon the shaft between the shoulderand the bush, and the adjustable spring operating upon the frame topress the roller 7U toward the conical surface of the head I, as and forthe purpose set forth. 11. In a constant-current electric motor, thecombination, with the armature-shaft and its bearings D, of the fixedbrushes 6 and e and the movable brush a, the commutator A, of suitablewidth to receive the brushes c and 0 side by side, the stud f, sustainedupon the bearing D and projected across the nearer side of thecommutator, the brush-holder f, pivoted upon the stud and holding thebrush e upon the farther side of the commutator, the swinging framehaving the seat (1', provided with the arms h, pivoted on ears j at theinner and outer sides of the bearing D, the stud d, projected from theframe over the nearer side of the commutator, the brushholder at,pivoted on such stud and holding the brush a upon the nearer side of thecommutator, and the adjustable spring 70, operating to press the frameforward to separate the brushes a and c, as and for the purpose setforth.

12. In a constant-current electric motor, the combination, with thearmature-shaft and its bearing D, of the fixed brushes 6 and e and themovable brush a, the commutator A, of suitable width to receive thebrushes a and 6 side by side, the stud f, sustained upon the bearing Dand projected across the nearer side of the commutator, the brush-holderf, pivoted upon the stud and holding the brush 6 upon the farther sideof the commutator, the swinging frame having the seat (Z, provided withthe arms 7L, pivoted on earsj at the inner and outer sides of thebearing D, the stud d, insulated upon the seat (1', the brush-holder a,carried upon a movable frame provided with roller 70, the governor-head6,

movable longitudinally upon the armatureshaft adjacent to the roller andhaving a conical surface to bear upon such roller, the governor-weightspivoted to such head and adapted when rotated to press the conicalsurface toward the roller, and a spring'acting in opposition to thecentrifugal force of the weights, as and for the purpose set forth.

13. In a constant-current electric motor, the combination, with thearmature, the armature-shaft, and its bearings, of the magnetcores 0,provided with the pole-pieces C the studs 0 projected from the bottomsof the cores through the bed and provided with the transverse pins (3*,cast within the core (l,recesses upon the under side of the bed aroundthe studs, and nut-s B fitted to the studs within the recesses to securethe cores upon the bed, as and for the purpose set forth.

14. In a constant-current electric motor, the combination, with thearmature, the armature-shaft, and its bearings, of the magnetcores 0,provided with pole-pieces C flanges C, and projecting studs 0 the bed B,with flat top and flat bottom, provided with the holes 13 and recessesB, and the nuts B ,fitted to screw-threads upon the studs within therecesses, as and for the purposes set forth.

15. In a constant-current electric motor having a portion of thearmature-coils shunted by the field, the combination, with the fixedbrushes 6 c and a movable brush a, operated as described, of aconnection from the movable brush to one of the field-coils,a switchhaving a switch-lever connected with one of the line-conductors, thecontact 1, connected with the other line-conductor and with the fixedbrush 6, the contact 3, connected with the fixed brush (2, and thecontact 2, connected directly with the other terminal of the field andindirectly through a resistance with the brush 6, as and for the purposeset forth.

16. In a constant-current electric motor having a portion of thearmature-coils shunted by the field, the combination, with the fixedbrushes 6 c and a movable brush a, operated as described, of aconnection from the movable brush to one of the field-terminals, aswitch having a switch-lever connected with one of the line-conductors,the contact 1, connected with the other line-conductor and with thefixed brush 0, the contact 3, connected with the fixed brush c, and. thecontact 2, having a plate 12 in contact with a block of resistingmaterial, and the opposite side of such resistance material beingconnected with the contact 3 by a connection y, as and for the purposeset forth.

17. In a constant-current electric motor having a portion of thearmature-coils shunted by the field, the combination, with the fixedbrushes c c and a movable brush a, operated as described, of aconnection from the movable brush to one of the field-terminals, aswitch having a switch-lever connected with one of the line-conductors,the contact 1, connected with the other line-conductor and with IIO thefixed brush 6', the contact 3, connected with the fixed brush 6, and thecontact 2, ha"- ing a plate 12 forming one side of the resistance-boxand connected directly with the other terminal of the field, the case11, with the block of resistance material R insulated from its sides,and the connection 3 from the bottom of the case to the contact 3, asand for the purpose setforth.

18. In a constant-current electric motor having a portion of thearmature-coils shunted by the field, the combination, with the fixedbrushes e e and a movable brush a, operated as'described, of aconnection from the movable brush to one of the field-coils, a switchhaving a switch-lever connected with one of the line-conductors, thecontact 1, connected with the other line-conductor and with the fixedbrush 6, the contact 3, connected with the fixed brush 6, and thecontact 2, connected directly with the other terminal of the field andindirectly through a resistance with the brush 6, and a cross-head 13upon the switchlever, adapted to join the contacts 2 and 3, as and forthe purpose set forth.

19. In a constant-current electric motor having a portion of the armature-coils shunted by the field, the combination, with the fixed brushes 6e and a movable brush a, operated as described, of a connection from themovable brush to one of the field-coils, the bedplate G, having thebinding-posts 4 5 6 7 connected with the field-coils and the brushes, as

described, the binding-posts 14 and 15 for the

